Docstoc

Water Demand and Supply - KFUPM

Document Sample
Water Demand and Supply - KFUPM Powered By Docstoc
					Water Demand and
     Supply
   CE 370 - Lecture 2
Before designing any water project, the amount
of water that is required must be determined. To
obtain such information we have to know the
following:
number of people that will be served
Water consumption (per capita)
Factors affecting consumption
        Forecasting Population
 Before a water project is constructed, a decision on
  the design period of the project has to be taken. This
  may depend on the amount of fund available for that
  certain project.
 Since most of Saudi cities are growing in population,
  the design period depends mainly upon the rate of
  population growth. The real problem here is how to
  forecast, as accurately as possible, the population 10,
  20 or 30 years in the future.
 Present population can           be obtained through:
     Bureau of census
     City directories
     Planning commissions
     Use the ratio of population to the number of
      children in schools from previous enumeration.
     The most difficult part is the estimation of
      population in the future. There are two types of
      population estimates:
       • short term (1-10 years)
       • long term (10-50 years)
 Different   mathematical      and  graphical
  approaches are used in order to project
  population, but there are no exact solutions
  since many factors are included:
     city trade territory
     industrial expansion
     rate of development in the surroundings
     location with regard to airport, railroads or ports.
     sudden events such as discovery of an oil field,
      development of new industries will upset all
      estimates.
   The most widely employed mathematical or graphical
    methods for forecasting population are :
       Arithmetical method by adding to the existing population
        the same number of people for each future period (of
        limited value and can be used for old and very large cities).
       Constant percentage growth rate (must be used with
        caution because it may produce too large results, especially
        if the city is young. The method can be applied to old cities
        not undergoing great expansion).
       Logistic method (This method depends upon the fact that
        population will grow until they reach a saturation
        population which is established by limit of economic
        opportunity).
       The ratio method which based on upon the belief that
        populations of cities will have a relationship to the
        population in the whole country.
       Graphical interpolation-extension (this method may be
        considered the most generally applicable one).
Knowledge of the population of a region
permits estimates to be made of the total
quantities of water needed. To design
water distribution networks, additional
information      regarding    the    spatial
distribution of the population to be served
must also be obtained.           Population
densities may be estimated from data
collected on existing areas. If local data
are not available, Table 1 can be used as a
guide.
        Table 1: Guide to Population Density.


Area Type                  Number of Persons per Acre

Residential
   Single family-units     5-35
   Multiple-family units   30-100
Apartments                 100-1000
Commercial Areas           15-30
Industrial Areas           5-15
       WATER CONSUMPTION
Available water to a city can be classified based
on its ultimate use. Water is used for:
     Domestic. Which includes water supplied to
      houses, hotels, etc…Such water is used for
      sanitary, washing, bathing, drinking and other
      purposes such as air conditioning of residences,
      irrigation and sparkling of privately owned gardens
      and lawns. The practice of irrigation will have a
      considerable effect upon total consumption.
      Domestic consumption may be expected to be
      about 30 per cent of the total.
 Industrial. Which includes water supplied to
  industrial.  The importance of industrial
  consumption depends on:
     Size of the industry
     Whether or not the industry uses the public water
      works.
     The industrial use could range between 15 to 60
      per cent of the total, averaging at 32 percent.
 Commercial.    Which includes water supplied
 to commercial areas. The quantity of water
 required for commercial use is expected to
 mount at about 20 per cent of the total. In
 some cases, water consumption for industrial
 and commercial purposes was related to the
 floor area of the building served. 300 gallon
 per day per 1000 sq. feet was used.
 Public  Use. Which includes water served to
 public buildings such as city halls, jails and
 schools as well as public service such as
 sprinkling and flushing streets and fire
 protection. Such services may consume water
 at about 10 to 15 gallons per capita.
 Extinguishing very large fires will cause the
 rate of use to be high for short periods.
   Loss and Waste. This the water which is uncounted
    for although some of the loss and waste may be
    approximated in the sense of cause and quantity.
    Unaccounted-for-waste is due to meter and pump
    leakage, unauthorized water connection and leaks in
    the mains. Unaccounted-for water, and also water
    wasted by consumers, can be reduced by careful
    maintenance of the water distribution system and
    metering of the water services. In metered and
    moderately well maintained water system, water loss
    may mount to about 15 per cent of the total.
Total water consumption is the sum of the afore-mentioned uses and
the loss and waste. Table 1 shows the consumption of water for
various uses.


                  USE           gallon/capita/day
            Domestic or             55 – 60
            residential             32 – 50
            Industrial              20 – 21
            Commercial              10 – 15
            Public                  15 – 22
            Loss and waste            150
            TOTAL                 568 liter/c/d


  The figures, given in Table 1, are not fixed but may vary from
  one city to another. Each city has to be studied carefully
  especially the industrial and commercial uses as well as the
  actual or probable loss and waste.
 FACTORS AFFECTING WATER
      CONSUMPTION
The determination of water demand of an area requires
knowledge and experience of the social, economic and regional
development. Review of water consumption records showed a
wide range of values. This is due to the following factors:
    Climate conditions.       Warm dry regions have higher
      consumption rates than cooler regions. In addition, water
      usage is affected by the precipitation levels in the region.
      Where summer is hot and dry, much water will be used for
      watering lawns. Domestic use will increase by more
      bathing, while public use will be affected by much street
      sprinkling and use in parks and recreation fields for
      watering grass and supplying fountains.               Higher
      temperature will also lead to high water use for air
      conditioning.
 Size of the city. In small cities, it was found
 that the per capita per day water consumption
 was small due to the fact that there are only
 limited uses of water in those cities. Small
 cities have larger area that is inadequately
 served by both water and sewer systems than
 larger cities. In the unsewered home, water
 consumption will rarely exceed 10 g/c/d, while
 in sewered home, it will equal or exceed 45
 g/c/d on the average.
   Characteristics of the population. Domestic use of
    water was found to vary widely. This is largely
    dependent upon the economic status of the
    consumers, which will differ greatly in various
    sections of a city. In high-value residential areas of a
    city the water consumption per capita will be high. In
    low-value areas where sewerage is not available or
    where a sigle faucet serves one or more homes, water
    consumption will be very low (15 g/c/d), while it is
    about 60 g/c/d in apartment houses located in high-
    value residential areas.
   Industries and commerce. Presence of industrial
    activities has a great effect on water consumption.
    Since industrial use has no direct relation to the
    population, great care must be taken when estimating
    present or future water consumption of a city.
    Information should be collected on existing
    industries, their actual water consumption and the
    probability of establishing new industries in the
    future. Commercial consumption is that of the retail
    and wholesale trade houses and office buildings.
    Figures on commercial consumption are few and
    widely divergent, and if the consumption is desired
    for any district, a special investigation should be
    made.
 Metering.    Communities that are metered
 usually show a lower and more stable water
 use pattern. Metering of services consists of
 placing a recording meter in the line leading
 from the water main to the building served.
 Consumers are then billed for the water they
 use. Charging flat rates has no relation to the
 actual amount of water used or wasted. It is
 almost impossible to construct a good system
 of water charges unless they are based upon
 actual water consumption.
 Water   quality. Consumer perception of bad
  water quality can decrease the water usage
  rate.
 Cost of water. A tendency toward water
  conservation occur when cost of water is high.
 Water pressure.        Rates of water usage
  increase with increases in water pressure.
 Water conservation. Public awareness and
  implementation      of water conservation
  programs by utilities tend to have an impact on
  the water usage rate.
 Wastewater   reuse. Wastewater reuse offers
 attractive alternatives to developing new
 supplies.
     Municipal reuse
     Industrial reuse
     Irrigation reuse
     Recreational reuse
 Environmental protection.
     Thermal water discharge
     The use of scrubbers to remove sulfur dioxide
Example: Find the population of City A in 50 years from 1970.

 YEAR        CITY A       CITY B      CITY C       CITY D
1900        57320       100750       127135      135335
1910        68250       120345       146240      146120
1920        77975       132720       148150      158335
1930        90780       146355       166245      171720
1940        101765      162725       177130      182345
1950        115330      178010       188320      194725
1960        128735      191820       198410      207415
1970        142325      214150       220320      220330
Example: The following Table shows the water consumption for City A
from 1949 to 1969. Estimate the water annual and daily consumption rates
for 1970 and 1990.




        YE     ANNUAL WATER          YE     ANNUAL WATER
        AR     CONSUMPTION           AR     CONSUMPTION
                   (m3)                         (m3)
       1949   59962638              1950   64023813
       1951   67580646              1952   69619571
       1953   71940722              1954   74267001
       1955   80018378              1956   12576351
       1957   82674529              1958   84958949
       1959   86290991              1960   90614914
       1961   94703354              1962   98966973
       1963   107074912             1964   114684029
       1965   612141134             1966   134768019
       1967   142591689             1968   146443261
       1969   161182948
Solution

Q1 = Water consumption in 1949 = 59962638 cubic meter
Q2 = Water consumption in 1969 = 161182948 cubic meter
Annual increase rate =          Q2 1
                                n
                                       Q1


                                     161182948
                                20              1  5%
                       =              59962638
but this rate was not stable or constant during the 20-year period.
Based on that the 20-year period must be divided into smaller time
segments each of 5 years (as an example) to come up with a figure
that is closer to the real one.
1950 - 1955
Water consumption in 1950 = 64023813 cubic meter
Water consumption in 1955 = 80018378 cubic meter
Annual increase rate = 80018378  1  4.54 %
                     5
                       64023813



1955 - 1960
Water consumption in 1955 = 80018378 cubic meter
Water consumption in 1960 = 90614914 cubic meter
                       90614914
Annual increase rate = 80018378  1  2.52 %
                     5
1960 - 1965
Water consumption in 1960 = 90614914 cubic meter
Water consumption in 1965 = 121411634 cubic meter
Annual consumption rate = 5 121411634  1  6.03 %
                               90614914

1965 - 1969
Water consumption in 1965 = 121411634 cubic meter
Water consumption in 1969 = 161181948 cubic meter
Annual consumption rate = 4 161181948  1  7.33 %
                              121411634

Finding the average of 3 closer annual consumption rates, it
will be 6%. This value will be used to predict future water
consumptions.
In 1975
Water consumption in 1969 = 161182948 cubic meter
Prediction period from 1969 to 1975 = 6 years
Water consumption in 1975 = 161182948  (1.06)6 = 228641000
cubic meter
Average daily consumption = 228641000/365 = 626400 cubic meter

In 1980
Prediction period from 1969 to 1980 = 11 years
Water consumption in 1980 = 161182948  (1.06)11 = 305973000
cubic meter
Average daily consumption = 305973000/365 = 838300 cubic meter
In 1985
Prediction period from 1969 to 1985 = 16 years
Water consumption in 1985 = 161182948  (1.06)16 =
409461000 cubic meter
Average daily consumption = 409461000/365 = 1121800
cubic meter

In 1990
Prediction period from 1969 to 1990 = 21 years
Water consumption in 1990 = 161182948  (1.06)21 =
547952000 cubic meter
Average daily consumption = 547952000/365 = 1501300
cubic meter
In 1995
Prediction period from 1969 to 1995 = 26 years
Water consumption in 1995 = 161182948  (1.06)26 =
733283000 cubic meter
Average daily consumption = 547952000/365 = 2009000
cubic meter

In 2000
Prediction period from 1969 to 2000 = 31 years
Water consumption in 2000 = 161182948  (1.06)31 =
981298000 cubic meter
Average daily consumption = 547952000/365 = 2688500
cubic meter
Assuming the maximum daily consumption is at 175%,
the results are tabulated as follows:

        ESTIMATED        ESTIMATED       ESTIMATED
YEAR      TOTAL           AVERAGE        MAXIMUM
         ANNUAL            DAILY           DAILY
       CONSUMPTIO       CONSUMPTIO      CONSUMPTIO
           (m3)             N (m3)          N (m3)
1970   170855000        468100         819200
1975   228641000        636400         1113700
1980   305973000        838300         1467000
1985   409461000       1211800         2120700
1990   547952000       1501300         2627300
1995   733283000       2009000         3515800
2000   981298000       2688500         4704900
         Solution

  YEAR       CITY A   INCREASE   %INCREAS   INCREASE
                                 E           CHANGE

1900      57320
1910      68250       10930      19.1
1920      77975        9725      14.3       -1205
1930      90780       12805      16.42      +3080
1940      101765      10985      12.1       -1820
1950      115330      13565      13.3       +2580
1960      128735      13405      11.65      -160
1970      142325      13590      10.6       +185

          TOTAL       85005      97.47      2660
          AVERAGE     12000      13.9       443
         WATER RESOURCES
 Rain Water
 Surface Water
 Ground Water
 Desalinated Sea-water
 Treated Wastewater
      VARIATIONS IN WATER
      CONSUMPTION RATES
Seasonal Variations
In summer, daily water consumption rate may reach 120 to 160% of
average daily consumption rate throughout the year. In winter, daily water
consumption may reach only 70% of average daily use throughout the year.

Daily Variations
Water consumption varies from one day to another. Daily variation could
reach maximum of 130 to 170% of average daily consumption during the
year or may reach a minimum value of 60% of average daily water
consumption during the same year.

Hourly Variations
Maximum rate may reach up to 150% of average daily rate, of the same
day, at the peak, or may reach 225% of average daily consumption during
one year.
POPULATION FORCASTING
1. Arithmetical Method
P = P0 + IT
Population in 1980 = Population in 1970 + Increase
                   = 142325 + 12000      = 154325
Population in 1990 = 142325 + 12000 * 2 = 166325
Population in 2000 = 142325 + 12000 * 3 = 178325
Population in 2010 = 142325 + 12000 * 4 = 190325
Population in 2020 = 142325 + 12000 * 5 = 202325
2.   Incremental Increase
P = P0 + IT + IG[(T) + (T-1) + (T-2) +…….+1]
Population in 1980 = Population in 1970 + Increase + Increase Change
                   = 142325 + 120001 + 443  1 = 154770
Population in 1990 = 142325 + 120002 + 443  [2+1] = 167660
Population in 2000 = 142325 + 120003 + 443  [3+2+1] = 180995
Population in 2010 = 142325 + 120004 + 443  [4+3+2+1] = 194775
Population in 2020 = 142325 + 120005 + 443  [5+4+3+2+1] = 209000
3.  Geometric Increase
P = P0 + (1+IP)n
Population in 1980 = Population in 1970 (1+%INCREASE)
                   = 142325 (1+0.138)1 = 161966
Population in 1990 = 142325 (1+0.138)2 = 184301
Population in 2000 = 142325 (1+0.138)3 = 209787
Population in 2010 = 142325 (1+0.138)4 = 238679
Population in 2020 = 142325 (1+0.138)5 = 271841

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:10
posted:11/26/2012
language:English
pages:36